1. Field of the Invention
Embodiments of the present invention are generally related to oil and gas drilling. More particularly, embodiments of the present invention pertain to pressure isolation plugs that utilize disintegratable components to provide functionality typically offered by frac plugs and bridge plugs.
2. Description of the Related Art
An oil or gas well includes a wellbore extending into a well to some depth below the surface. Typically, the wellbore is lined with a string of tubulars, such as casing, to strengthen the walls of the borehole. To further reinforce the walls of the borehole, the annular area formed between the casing and the borehole is typically filled with cement to permanently set the casing in the wellbore. The casing is then perforated to allow production fluid to enter the wellbore from the surrounding formation and be retrieved at the surface of the well.
Downhole tools with sealing elements are placed within the wellbore to isolate the production fluid or to manage production fluid flow into and out of the well. Examples of such tools are frac plugs and bridge plugs. Frac plugs (also known as fracturing plugs) are pressure isolation plugs that are used to sustain pressure due to flow of fluid that is pumped down from the surface. As their name implies, frac plugs are used to facilitate fracturing jobs. Fracturing, or “fracing”, involves the application of hydraulic pressure from the surface to the reservoir formation to create fractures through which oil or gas may move to the well bore. Bridge plugs are also pressure isolation devices, but unlike frac plugs, they are configured to sustain pressure from below the plug. In other words, bridge plugs are used to prevent the upward flow of production fluid and to shut in the well at the plug. Bridge plugs are often run and set in the wellbore to isolate a lower zone while an upper section is being tested or cemented.
Frac plugs and bridge plugs that are available in the marketplace typically comprise components constructed of steel, cast iron, aluminum, or other alloyed metals. Additionally, frac plugs and bridge plugs include a malleable, synthetic element system, which typically includes a composite or synthetic rubber material which seals off an annulus within the wellbore to restrict the passage of fluids and isolate pressure. When installed, the element system is compressed, thereby expanding radially outward from the tool to sealingly engage a surrounding tubular. More recently, frac and bridge plugs have been developed with sealing elements, including cone portions and seal rings made of composite material, like fiber glass and a matrix, like epoxy. The non-metallic portions facilitate the drilling up of the plugs when their use is completed. In some instances, the entire body or mandrel of the plug is made of a composite material. Non-metallic elements are described in U.S. Pat. No. 6,712,153 assigned to the same owner as the present application and the '153 patent is incorporated by reference herein in its entirety. Typically, a frac plug or bridge plug is placed within the wellbore to isolate upper and lower sections of production zones. By creating a pressure seal in the wellbore, bridge plugs and frac-plugs isolate pressurized fluids or solids. Operators are taking advantage of functionality provided by pressure isolation devices such as frac plugs and bridge plugs to perform a variety of operations (e.g., cementation, liner maintenance, casing fracs, etc.) on multiple zones in the same wellbore—such operations require temporary zonal isolation of the respective zones.
For example, for a particular wellbore with multiple (i.e., two or more) zones, operators may desire to perform operations that include: fracing the lowest zone; plugging it with a bridge plug and then fracing the zone above it; and then repeating the previous steps until each remaining zone is fraced and isolated. With regards to frac jobs, it is often desirable to flow the frac jobs from all the zones back to the surface. This is not possible, however, until the previously set bridge plugs are removed. Removal of conventional pressure isolation plugs (either retrieving them or milling them up) usually requires well intervention services utilizing either threaded or continuous tubing, which is time consuming, costly and adds a potential risk of wellbore damage.
Certain pressure isolation plugs developed that hold pressure differentials from above while permitting flow from below. However, too much flow from below will damage the ball and seat over time and the plug will not hold pressure when applied from above.
There is a need for a tool for use in a wellbore having a flow path that is initially blocked and then opened due to the dissolution of a disintegratable material. There is a further need for a pressure isolation device that temporarily provides the pressure isolation of a frac plug or bridge plug, and then allows unrestricted flow through the wellbore. One approach is to use disintegratable materials that are water-soluble. As used herein, the term “disintegratable” does not necessarily refer to a material's ability to disappear. Rather, “disintegratable” generally refers to a material's ability to lose its structural integrity. Stated another way, a disintegratable material is capable of breaking apart, but it does not need to disappear. It should be noted that use of disintegratable materials to provide temporary sealing and pressure isolation in wellbores is known in the art. For some operations, disintegratable balls constructed of a water-soluble composite material are introduced into a wellbore comprising previously created perforations. The disintegratable balls are used to temporarily plug up the perforations so that the formation adjacent to the perforations is isolated from effects of the impending operations. The material from which the balls are constructed is configured to disintegrate in water at a particular rate. By controlling the amount of exposure the balls have to wellbore conditions (e.g., water and heat), it is possible to plug the perforations in the above manner for a predetermined amount of time.
It would be advantageous to configure a pressure isolation device or system to utilize these disintegratable materials to temporarily provide the pressure isolation of a frac plug or bridge plug, and then provide unrestricted flow. This would save a considerable amount of time and expense. Therefore, there is a need for an isolation device or system that is conducive to providing zonal pressure isolation for performing operations on a wellbore with multiple production zones. There is a further need for the isolation device or system to maintain differential pressure from above and below for a predetermined amount of time.